Aliphatic acid process



llnite States PatentO .ifiWEfi-il Emil F. .iason and K. Fields, Chicago,lil to tandard {Bil Company, Chicago, ill, a corporation oi lnliana NoDrawing. Filed June 363, i959, filer. N $23,863

6 Claiins. (Cl. ass-ass) a liquid phase to o. dation with molecularoxygen. By these processes acidic oxidation products result. The

oxidation products have generally been mixtures of allphatio11lOIlCCEiIb$-i to acids of varying chain length and in some cases areeven aliphatic dicarboxylic acids. When saturated parafdnic hydrocarbonsare oxidized in a cat ytic liquid phase system under selectedtemperature conditions and controlled rate of addition of rnol cularoxygen, in general, these pr cesses produce mainly carbon monoxide,carbon dioxide, water, formic acid and acetic acid. In many of theprocesses for oxidizing aliphatic hydrocarbons in the liquid phase withair, especially where monocarboxylic acids were oduced, the acidicproducts were formed in admixt re with darkcolored resinous polymerizedmaterials which precluded recovery or the desired acids as satisfactory,useful products. To avoid the torn n of such contaminants, low oxidationtemperatures r low conversions Were suggcsted to obtain onl" pa; 1oxidation of the aliphatic hydrocarbon feed stock. However, the use ofeither or both or these means to avoid the dark-colored high molecularweight contaminants in -T-Ledly reduces the reaction rates, thusresulting in relatively long reaction periods. The use of variousspecial catalyst, promoters and special apparatus, together with theselected operating conditions, have been proposed to obtain especiallylong chain aliphatic monocarboxylic acids. However, no commercialprocess is available for producing and readily recovering relativelylong chain aliphatic monocarboxylic acids by the oxidation of aliphatichydrocarbons with air in a liquid phase process.

It has now be n discovered that alkene-l hydrocarbc'i containing 3 to 20or more carbon atoms can be oxidized in a liquid phase with molecularoxygen in the presence of a c; 'alyst comprising bromine and a heavymetal catalyst to produce a normal aliphatic nionocarboxylic acidproduct containing one less carbon atom than present in the allrene-lhydrocarbon. When the fllliBYiG-l. hydrocarbon is a normal alliene-lcontaining at least five carbon atoms, there is produced a mixturecontaining the normal aliphatic monocarboxylic acid of one less carbonatom and lreto, i.e., acetyl, derivave thereof. Allrene-l hydrocarbonsof less than five carbon atoms; i.e., two to four carbon atoms oxidizeto produce normal aliphatic monocarboi-zylic acids as the product. Thus,when normal allzene-l hydrocarbons,

o.'r,-(crr wherein n is a number of from t) to 17 or higher, areoxidized, the aliphatic monocarboxylic acid product is, when n is 0,acetic acid; a is 1, propionic acid; it is 2, n-butyric acid and acetylacetic acid; it is 3, n-valeric acid and 3-acetyl propionic acid; it is4, u-uexanoic acid and 4-acetyl butyric acid; it is 5, u-heptanoic andS-acetyl pen'tanoic acid; etc. Branched chain allrene-l hydrocarbonshaving the formula:

R R oir -t l(t ilmoir=om I l/Z Iii! wherein "3 R R and R are hydrogen ormethyl and at least one of R or R or R or R is meth 'l and m is a numberfrom (i to 16 or higher; i.e., a branched chain allzene-l hydrocarboncontaining live or more carbon atoms can also be oxidized according tothe process of this invention to aliphatic monocarboxylic productscontaining the aliphatic monocarboxylic acid of one less carbon atomthan the sllrene-l. When both R and R are hydrogen, then a ketoaliphatic acid will also be formed. ccompanying lay-products of theoxidation are carbon monoxide, carbon dioxide, Water, formic acid andacetic acid. Since acetic acid and propionic acid are readily availablefrom other processes, the process of this invention is preferablycarried out with normal allrene-l hydrocarbons and their methylsubstituted derivatives which contain a terminal -CHCH group as thestool: to be oxidized. These allzene-l hydrocarbons vvill contain fiveor more carbon atoms. The alkene-l hydrocarbons containing both a Cl-lCH group and a CH:Cl-l group terminal groups are preferred for thepreparation of acetyl aliphatic monocarooxylic acids and aliphaticmonocarboxylic acids of one less carbon atom than the feed stool;alkene-l.

The present process conducted in the maid p rose at a temperature below200 (3., preferably at a temperature in the range of about 50 to 295 C.The temperature at which the process is carried out will determine to anappreciable extent the minimum pressure to be employed to maintainliquid phase of the reaction mixture. The pressure at any specifictemperature will be governed by the vapor pressures of the materials inthe reaction miature. When the reaction mixture contains the allrene-lhydrocarbon, the pressure to be maintained will be that required to keepat least a portion or" the alkene-l in the liquid phase. it isadvantageous during the course of the reaction to subject the vapors incontact with the reaction mixture to partial condensation to condenseout of vapors at least the alkened hydrocarbon contained therein.However, there are also advantages in carrying out the process of thisinvention in the presence of a reaction solvent or diluent. For thispurpose any inert solvent may be employed. it is preferred that thesolvent or reaction medium dissolve at least a portion of the alliene-lbeing oxidized and also dissolve the heavy lvionocarboxylic acidsconmetal oxidation catalyst. taining 2 to 8 carbon atoms can be used asreaction solvents or reaction media. Such monocarboxylic acids includebenzoic acid and the lower aliphatic monocarboxylic acids such as aceticacid, propionic acid, butyric acid, Valerie acid, ens-.nthic acid andcaprylic It will be appreciated that many of these acids are produced inthe process of this invention. Whether or not the acids see as thereaction solvents or reaction media are produced in the process of thisinvention, the separation of the desired products from the reactionmixture can be readily accomplished. Because of its resistance tooxidation under the conditions of the process of this invention, aceticacid is the preferred lower aliphatic monocarboxylic acid for use as thereaction solvent or reaction medium.

The use of such a reaction solvent or reaction medium either permits aconvenient means for removing heat of reaction since the vaporizedreaction solvent can be condensed and returned to the liquid phase or,in the case of morass-2 the use of the higher boiling rnonocarboxylicacids, a. lower pressure reaction can be conducted and still main-- tainthe liquid phase.

Air is the most readily available source of molecular oxygen. However,substantially pure oxygen; i.e., commercial oxygen, oxygen plus ozone,mixtures of oxygen. and inert gas, and mixtures of air and inert gasescan be employed as the source of molecular oxygen for the process ofthis invention. Molecular oxygen-containing gases having from 5% to 100%oxygen by volume can. be employed.

in the practice of this invention the catalyst system comprises bromineand a heavy metal oxidation catalyst. The bromine may be employed aselemental, combined,

or ionic bromine. More spechically, as a source of br0- mine for thecatalyst system there may be employed molecular bromine, ammoniumbromide, hydrogen bromide, and other bromine-containing compoundssoluble in the reaction mixture. Satisfactory results can be obtained,for example, by the use of potassium bromate, tetra-- bromoethane,benzyl bromide and the like as a source of bromine.

The heavy metal oxidation catalyst portion of the catalyst systememployed in the process of this invention includes the heavy metals andderivatives thereof which are soluble in the reaction medium to theextent necessary to provide a catalytically effective amount of theheavy metal oxidation catalyst component. The term heavy metal isemployed herein in the same sense as employed in connection with themetals shown in the Periodic Chart of Elements, appearing on pages 56and 57 of the Handbook of Chemistry, 8th edition, published by HandbookPublishers, Inc, Sandusky, Ohio (1952). From this group there have beenfound heavy metal oxidation catalysts desirably applicable to theprocess of this invention for furnishing the heavy metal oxidationcomponent of the catalyst system. Of the heavy metal group, those metalshaving an atomic number not greater than 84 have been found most useful.Excellent results are obtained by the utilization of metals having anatomic number of from 23 to 28 inclusive. Particularly excellent resultsare obtained with a metal of the group consisting of manganese, cobalt,nickel, iron, chromium, vanadium, molybdenum, tungsten, tin and cerium.The catalytic amount of the heavy metal may be provided either by asingle metal or a combination of the metals. The heavy metal oxidationcatalyst component of the catalyst system in the process of thisinvention may be provided by the addition of the metal in elementalform, as its oxide or hydroxide, or in the form of a salt of the metal.For example, the metal manganese may be employed as the manganese saltof an organic carboxylic acid, such as manganese naphthenate, manganesetoluate, manganese acetate, etc., or in the form of an organic complex,such as the acetylacetonate, the 8-hydroxy-quinolate and the ethylenediarnine tetra-acetate, as well as inorganic manganese salts such as theborates, halides and nitrates. The catalyst system may also be providedby the use of a heavy metal bromide or mixtures of heavy metal bromides.

The amount of metal catalyst employed is not critical and may be in therange of about 0.01 to about by weight or more based on the feed stockreactant. Where the heavy metal is introduced as a bromide salt, forexample as manganese bromide, the proportions of manganese and bromineWill be in their stoichiometric proportions. The ratio of metal tobromine may be varied from such proportions Within the range of about 1to 10 atoms of heavy metal oxidation catalyst per atom of bromine toabout 1 to 10 atoms of bromine per atom of heavy metal.

The amount of solvent or reaction medium employed will vary over Widelimits as will be readily appreciated by those skilled in the art. Theamount of solvent or reaction medium employed is not critical buttypically will l be in the range of from about 0.1 to about 10,desirably 0.5 to 4 times the weight of oxidizable feed stock.

In order to facilitate a clear understanding of the invention, theprocess of this invention is illustrated by the following preferredembodiments described in detail.

Example I As an oxidation reactor there is employed a vertical tubularreactor into the bottom of which air or other source of molecular oxygencontaining gas can be charged. The bottom of said reactor is alsosuitably adapted to the removal of the mixture resulting from theoxidation process. The top of the reactor is provided with a means forclosing the reactor through which is connected a vapor line for transferof vapors to a condenser from which condensate may be recycled to thereaction zone. A condenser is provided with means for removing theuncondensed materials through a pressure regulating valve with which thereaction pressure is maintained to obtain a liquid phase throughout thereaction. The reactor is constructed of corrosion-resistant materialsuch as highly corrosive resistant alloys, or is glass-lined. To such areactor there is charged a mixture containing 112.2 grams (1 mole) ofl-octene, 120.1 grams (2 moles) glacial acetic acid and 10 millilitersof an aqueous solution containing cobalt acetate and manganese acetate,each in a 0.25 molar concentration. There is also added 1.0 milliliterof 5 molar ammonium bromide dissolved in Water. The resulting mixture isheated to 170 C. in the presence of sulficicnt nitrogen so that theresulting pressure is 400 p.s.i.g. Air at a pressure of about 4-00p.s.i.g. is introduced into the reactor at a flow rate of about 3 litersper minute. After 5 hours of air addition, the reactor conteuts arecooled and distilled.

As a first fraction there are collected all materials boiling up to 50C. at mm. Hg. This mixture contains primarily formic acid, acetic acidand water. The total amount of acetic acid collected in this mixture is128 grams.

As a second fraction there is collected material boiling in the range of63 C. at 2.2 mm. Hg to 94 C. at 1.8 mm. Hg. This fraction whenredistilled has a boiling point of 200203'. C. and has a refractiveindex of n of 1.4218. This second fraction is n-heptanoic acid for whichthe literature reports a boiling point of 202 C. and a refractive indexof n of 1.4216.

As a third fraction there is collected material boiling at 121143 C. at1.7 mm. Hg. This material has a refractive index of 11 of 1.4464.Analysis of this material (third fraction) shows 60.0% carbon and 9.4%hydrogen. The neutral equivalent of this fraction is 146. Acetylpentanoic acid has a calculated neutral equivalent of and a calculatedcarbon and hydrogen content of 58.0% and 9.0%, respectively. The thirdfraction is substantially all S-acetyl pentanoic acid.

Only a small amount of residue remains, about 7.3 grams, which was notfurther characterized.

When the process of the foregoing example is carried out at atemperature of C., the yield of n-heptanoic acid is increased, and theyield of the keto-acid is decreased. By carrying out the process of theforegoing example at a temperature of about to C., the yield of theketo-acid is increased while the yield of nheptanoic acid is decreased.

The use of manganese bromide in place of ammonium bromide in the processof the foregoing example in an amount to provide an equivalent amount ofmetal will produce substantial? equivalent results. Also in place ofemploying both manganese acetate and cobalt acetate there may beemployed either manganese acetate or cobalt acetate. Other members ofthe heavy metal oxidation catalyst can be employed to producesubstantially the same results.

As additional feed stocks of the process o this invention there may bespecifically employed l-hexene, 3,3-dimethyl hexene-l, l-decene,l-hexadecene, l-heptadecene, and the like.

What is claimed is:

l. A process for the preparation of saturated normal aliphaticmonocarboxylic acid products of from 4 to 19 carbon atoms whichcomprises oxidizing in the liquid phase an alkene-l hydrocarboncontaining 5 to 20 carbon atoms with molecular oxygen at a temperaturein the range of 50 to 200 C. in the presence of a catalyst consistingessentially of bromine and a heavy metal oxidation catalyst anddistilling the resulting reaction mixture to recover the resultingsaturated normal aliphatic monocarboxylic acids.

2. The process of claim 1 wherein air is the source of molecular oxygen.

3. A process for the preparation of saturated normal aliphaticmonocarboxylic acid products of from 4 to 19 carbon atoms whichcomprises oxidizing in the liquid phase an alkene-l hydrocarboncontaining 5 to 20 carbon atoms with molecular oxygen at a temperaturein the range of 50 to 200 C. in the presence of a monocarboxylic acid offrom 2 to 8 carbon atoms selected from the class consisting of benzoicacid and lower alkanoic acids and in the presence of a catalystconsisting essentially of bromine and a heavy metal oxidation catalystand distilling the resulting reaction mixture to recover the resultingsaturated normal aliphatic monocarboxylic acids.

4. A process for the preparation of saturated normal aliphaticmonocarboxylic acid products of from 4 to 19 carbon atoms whichcomprises oxidizing in the liquid phase an alkene-l hydrocarboncontaining 5 to 20 carbon atoms with molecular oxygen at a temperaturein the range of 50 to 200 C. in the presence of acetic acid and in thepresence of a catalyst consisting essentially of bromine and a heavymetal oxidation catalyst and distilling the resulting reaction mixtureto recover the resulting saturated normal aliphatic monocarboxylicacids.

5. The process for the preparation of a mixture of normal aliphaticmonocarboxylic acid products containing a normal aliphaticmonocarboxylic acid and a keto derivative thereof having the respectiveformulae:

GOOH

wherein n is an integer of from 1 to 16 by oxidizing in the liquid phasean alkene-l hydrocarbon containing 5 to 20 carbon atoms with molecularoxygen at a temperature of from about C. to about 200 C. in the presenceof acetic acid and in the presence of a catalyst consisting essentiallyof bromine and a heavy metal oxidation catalyst, distilling theresulting reaction mixture to remove a mixture containing acetic 'acidand. low boiling reaction by-products, which mixture is characterized byboiling up to 50 C. at mm. Hg, and recovering from the residue saidaliphatic acid and its keto derivative.

6. The process for preparing heptanoic acid and 5- acetyl pentanoic acidcomprising oxidizing octene-l in the liquid phase with air in thepresence of acetic acid and in the presence of a catalyst consistingessentially of bromine and a heavy metal oxidation catalyst at atemperature of from about 50 to about 200 C., distilling the resultingreaction mixture to remove a mixture characterized by boiling up to 50C. at 140 mm. Hg. and containing acetic acid, formic acid and water, anddistilling the residue to recover heptanoic acid and S-acetyl pentanoicacid as separate products.

References Cited in the file of this patent UNITED STATES PATENTS Rustet a1. Feb. 13, 1945 Saffer et al. May 6, 1958 OTHER REFERENCES

1. A PROCESS FOR THE PREPARATION OF SATURATED NORMAL ALIPHATICMONOCARBOXYLIC ACID PRODUCTS OF FROM 4 TO 19 CARBON ATOMS WHICHCOMPRISES OXIDIZING IN THE LIQUID PHASE AS ALKENE-1 HYDROCARBONCONTAINING 5 TO 20 CARBON ATOMS WITH MOLECULAR OXYGEN AT A TEMPERATUREIN THE RANGE OF 50* TO 200*C. IN THE PRESENCE OF A CATALYST CONSISTINGESSENTIALLY OF BROMINE AND A HEAVY METAL OXIDATION CATALYST ANDDISTILLING THE RESULTING REACTION MIXTURE TO RECOVER THE RESULTINGSATURATED NORMAL ALIPHATIC MONOCARBOXYLIC ACIDS.